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Start with the spacing, not the shape

Contour lines join points of equal height. On a 1:25,000 map, they are usually drawn at 10-metre vertical intervals. That number is your key. The closer the lines, the steeper the ground. If you can lay a thumb between two contours, the slope is gentle. If the lines touch or merge into a black mass, you are looking at a cliff or a very steep face.

Wide spacing often means a plateau, a boggy top, or a broad ridge. Tight spacing means a pull; very tight spacing may need hands, or should be avoided. Before you plan an ascent, scan the slope and ask: where are the contours packed, and where do they relax?

Hachures, crags and the language of steep ground

Contours give the shape; hachures give the texture. Hachures are the short black lines that run down the fall line on steep ground, especially crags. They point downhill. If hachures point towards you as you look at the map, you are standing below a crag. If they point away, you are above it. That simple check can save you from walking over an edge in mist.

Crag symbols are your warning. A band of black shading with hachures means rock. It might be a small outcrop, or a continuous face. Look for breaks: a gully, a chimney, or a ridge line. Ridges are often the safest way up because they are drier and less loose than gullies. Gullies can be loose, vegetated, or snow-filled. They also funnel you into a trap if the ground steepens above.

• V pointing uphill shows a re-entrant or gully. Water and rock gather there.
• V pointing downhill shows a spur or ridge, usually better underfoot and a natural line of ascent.
• Contours forming a bowl suggest a corrie, often with crags at the head. Plan around it.

Use grid lines to measure distance and gradient

Grid lines are the quiet workhorses of route planning. On a 1:25,000 map, they are 1 kilometre apart. That gives you a ready-made ruler. Count the contours you cross between two points, multiply by 10 metres, and you have the total ascent. Then compare that rise with the horizontal distance from the grid lines.

Cross five contours in half a grid square and you have 50 metres over 500 metres, or 1 in 10. That is a steady pull. Ten contours in the same half-square is 1 in 5, a stiff climb. Twenty in a quarter-square is 1 in 1.25: a scramble or a crag. If your line crosses that, find another.

Use the grid to estimate time. Naismith's rule: one hour per 5 kilometres, plus one hour per 600 metres of ascent. Add time for rough ground, bog, and a heavy pack. Contour counting turns "it looks steep" into a number.

Read the whole hillside, not just the slope

Contours describe the shape of a hillside. A convex slope has contours that are wider at the top and tighter at the bottom. It eases off as you climb. A concave slope is the opposite: gentle at the bottom, steepening as you go. Uniform spacing means a constant gradient. None of these are good or bad on their own, but they change how a climb feels and how much effort it takes.

Look for larger features: a saddle or col often gives a natural, sheltered route. A spur can be a handrail of higher ground. A valley may offer a gentle descent, but check it does not narrow into a gorge. Streams, walls, and fences are useful handrails, but they can also lead you into steep ground. Follow them on the map first.

Escape routes, weather and the final check

Before you leave the car, trace your route and mark tick features: a col, a stream junction, a wall corner, a distinct contour shape. Then trace an escape route. If the weather turns or the ground is steeper than expected, where can you go? A broad spur, a gentle valley, or a traversing path are better than forcing a line up a crag.

Weather changes the meaning of contours. A 1 in 5 slope of wet grass can be treacherous. Snow and ice turn a summer walk into winter mountaineering. Contours do not show rock type, vegetation, or looseness. Use guidebooks and local knowledge. If the map shows tight contours, hachures, and no obvious break, choose another line. The hills will still be there.

Practise on a familiar hill

Take a 1:25,000 map to a familiar hill. Find a slope you have walked before. Count the contours, check the hachures, and compare map with ground. Notice where the map made the slope look easy and where it hid a steepening. Build the habit of reading the land before you walk it.

On the day, keep matching map to ground. If the contour shape does not fit what you see, stop and relocate. Contour reading grows with use. The more you practise, the more the map becomes a picture of the hillside, and the safer your routes.